Shoulder preparation of teeth



April 1, 8 w. c. ASHKIN 2,828,544

SHOULDER PREPARATION OF TEETH Filed July 13, 1955 INVENTOR WILL/AM C. ASHK/N ATTORNEY United rates Patent SHOULDER PREPARATIGN {)F TEETH William C. Ashkin, New York, N. Y.

Application July 13, 1955, Serial No. 521,761

2 Claims. (Cl. 32-58) This invention relates to new and useful improvements in the shoulder preparation of teeth.

In dentistry, in order to fit teeth with crowns or porcelain jackets, it is first necessary to grind away a portion of the upper surface of the tooth and to leave a squarecut shoulder at about the gum line. The crown or jacket is then fitted over the reduced portion of the tooth, so that the same rests on the shoulder, and is then secured in this position. The formation of this shoulder with the grinding away of a portion of the upper surface of the tooth is known in the dental art as the shoulder preparation of the tooth.

In the past, the shoulder preparation of the tooth was etfected by means of a free hand-grinding, using small abrasive grinding wheels, and/ or discs, such as diamond wheels or discs.

In order to efiect this grinding, a good deal of manual dexterity and skill was required on the part of the dentist, and it was extremely diflicult to get an even and square shoulder, particularly at those portions about the circumference of the tooth which were difiicult to reach and see. Very often, in attempting to grind tthe shoulder, the dentist would grind too deeply, causing injury to the remaining tooth portion, or would form an irregular shoulder, which would not provide a satisfactory base for the crown or jacket.

One object of this invention is a method and a device which will allow an extremely uniform and accurate tooth-shoulder preparation and which requires a minimum of manual dexterity and skill. This, and still further objects will become apparent from the following descriptions, read in conjunction with the drawings, in which:

Fig. 1 is a plan view of an embodiment of a clamp in accordance with the invention for aiding in the shoulder preparation of teeth;

Fig. 1a is an exploded perspective view of a portion of a different embodiment of a clamp corresponding to the clamp in Fig. 1 with a removable exchangeable toothengaging guide plate, tongue depressor, and cheek retractor.

Fig. 2 is a side elevation of the clamp shown in Fig. 1 positioned on a tooth;

Fig. 3 is a front elevation of the clamp shown in Fig. 2;

Fig. 4 diagrammatically shows a front elevation of the tooth with the attached clamp arrangement as shown in Figs. 2 and 3, having a groove ground therein.

Fig. 5 diagrammatically shows a front elevation of the grooved tooth of Fig. 4, having its side wall ground down, using the clamp of Figs. 1, 2, and 3;

Fig. 5a is a side elevation showing a tapered grinding wheel corresponding to the grinding wheel shown in Fig. 5.

Fig. 6 is a front elevation of the tooth after the shoulder preparation in accordance with the invention; and

2,828,544 Patented Apr. 1, 1958 "ice Fig. 7 is a front elevation of a tooth illustrating the grinding down of an over-hanging portion, using the clamp of Figs. 1, 2, and 3 prior to the grooving.

In accordance with the invention, the shoulder is prepared on the tooth with the aid of a substantially flat guide surface, which is positioned at about the gum line of the tooth and which extends along opposite sides of the tooth in a plane substantially normal to the tooth axis. The flat guide surface is preferably established with the aid of a clamp, as, for example, is shown in Fig. 1 of the drawings.

The clamp has two opposing, tooth-engaging guide plates 2, which are dimensioned along their inner concave tooth-engaging edges 1 for engaging opposite sides of a tooth, such as the tooth 8, at about the gum line. The guide plates 2 have substantially flat guide surfaces which extend in a plane substantially normal to the tooth axis when the clamp is in tooth-engaging position. The tooth-engaging guide plates 2 should preferably be large enough, so that they can extend along and engage substantially the entire lingual and opposed side of the tooth.

The tooth-engaging plates 2 are mounted on the ends of the clamp arms 3, which are pivotally connected together at the pivot joint 4. A spring 5 tends to resiliently urge the arms 3 apart. A guide rod 6 with the thumb screw 7 is connected to the arms 3, so that the same may be forced together into tooth-engaging position by turning the thumb screw 7.

The tooth-engaging plates 2 may be formed integral with the clamp arms 3, as for example, by grinding, or, in accordance with a preferred embodiment of the invention, may be made detachably connected to the clamp I arms, so that the same may be interchanged for toothengagement plates dimensioned for engaging teeth of different sizes. The detachable arrangement may be effected in any known or conventional manner. As shown in Fig. 1a, the tooth-engaging clamp of different size from the one shown in Fig. 1 has a socket of rectangu lar cross-section extending therethrough, which may be slipped over in engagement with the end of the arm'3, which is in the form of a prong. The tooth-engaging plate may thus be removed and replaced with a toothengaging plate on a ditferent size, as, for example, dimensioned for a smaller or larger tooth. Additionally to facilitate manipulations in the patients mouth, a detachable tongue-depressor 27 and cheek retractor 28 may be provided. The tongue-depressor and cheek retractor are provided with two spaced-apart sockets which correspond to the single socket on the plate 2 so that when positioned on the prong 5, they will straddle the socket of the plate 2.

The arms 3, as may be seen in Fig. 2, are bent at 9 and reverse bent at 10, so that the same are bent in a Z-form out of the plane of the guide plates 2.

As may be seen from Fig. 3, the arms 3 extend through slots 11 and 12, respectively, which are provided through the guide bar 6. The thumb screw 7 extends into the slot 12, so that by screwing the thumb screw 7 in, the arm 3 at the lefthand side of the drawing will be forced toward the righthand end of the slot 12, thus bringing the arms 3 toward each other and the tooth-engaging guide plates 2 into engaging position.

Conversely, as the thumb screw 7 is unscrewed, the spring 5 will force the arm 3 at the lefthand side of the drawing toward the lefthand side of the slot 12, causing the arms 3 to move apart and releasing the clamp.

Any other desired or conventional arrangement for bringing the arms 3 together or separating the same may, of course, be used in place of the arrangement 6--7.

As may be seen, the clamp is in the form of a caliper and will be referred to herein as a caliper clamp.

In operation, the front screw 7 is unscrewed, So that the spring will force the arms 3 apart, so that the distance between'the tooth-engaging edges 1 is greater than the width of the tooth.

The clamp as is shown in Fig. 2 is then slipped over the tooth 8. Due to the Z -bend of the arms 3, the clamp will pass free of the other teeth in the mouth and may be very accurately positioned so that the tooth-engaging guide plates 2 are at the gum line, even if the tooth S is crooked or the like. The thumb screw 7 is then tightened, forcing the arms 3 together, and bringing the engaging edges 1 in engagement with the tooth 8 at the gum line, and securing the clamp tight.

A groove is then cut in the tooth at the gum line with aid of the cylindrical grinding wheel 13. The grinding wheel 13 has a fiat base 14, which is free of abrasive and defines a lower guide surface. The grinding wheel 1?: is mounted on a shaft which is fitted in the conventional dentist drill holder 16. The depth of the groove is determined by the distance a which the grinding wheel 13 extends past the shaft 15. The grinding wheel 13 has an abrasive surface, such as a diamond abrasive surface at its outer cylindrical grinding surface. In operation, the grinding wheel 13 is pressed with its lower guide surface 14 in contact with the guide plates 2. The surface of the guide plate 2 which contacts 14 is hat and extends in a plane substantially normal to the tooth axis. The vertical positioning of the grinding wheel 13 with respect to the tooth is thus positively established and cannot vary as long as the surface 14 is maintained in contact with the plate 2. The grinding wheel 13 is then caused to rotate and pressed against the tooth. The same will cut a groove 17 into the tooth to a depth equal to the distance :1. Once this depth is reached, the shaft 15 will contact the side wall of the tooth, so that the grinding wheel cannot cut any deeper. The grinding wheel is moved along the plates 2, cutting the groove 17 along the entire lingual and buccal or labial side of the tooth. The groove 17 is completely uniform and at the exact vertical position, due to the positioning of the plates 2. Further, the depth of the groove 17 is completely uniform, being equal to the depth a.

After the groove 17 has been cut, the cylindrical grinding wheel 13 is replaced by a second cylindrical grinding wheel 18.

The second grinding wheel 18 is of greater axial height than the axial height of the grinding wheel 13, and should extend over the entire axial height of the tooth 3. The grinding wheel 18 has lower guide surface 19 similar to the guide surface 14. Extending above the guide surface 19 is a cylindrical portion 29 which is free from abrasion. This cylindrical portion may have any height which is equal to or less than the axial height of the first grinding wheel 13. The portion above the abrasive free portion 20 has an abrasive coating such as a diamond coating similar to the coating on the grinding wheel 13. The grinding wheel 18 is mounted on a shaft 21, which is positioned in the drill holder 16 and rotated. The guide surface 19 is pressed against the flat surface of the plate 2 in the same manner as the surface 14 was in connection with the grinding wheel 13. The grinding wheel 18 is then brought in contact with the tooth 8 and will grind away the side wall portion of the tooth above the groove 17. Once, however, the side wall portion is cut away to the depth of the groove 17, the abrasive free portion 20 will contact the inner surface of the groove 17, which will prevent further grinding away of the tooth. In this manner, the entire upper diameter of the tooth is ground down to the depth of the groove 17, taking the form as shown in Fig.

In order to prepare the tooth for the crown or Jacket, it is often desirable to taper the tooth so that the same decreases in cross-section in a direction away from the gum line. In order to effect this tapering, the grinding wheel 13 may have a frusto-conical shape as shown in Fig. 5a.

The interproximal sides of the tooth, i. e., the mesial and distal sides can generally not be ground in this manner, since there is generally not enough clearance between the adjacent teeth. In order to effect the grinding of the intcrproximal sides of the tooth, a conventional thin abrasive disc, such as a diamond disc is used. The ends 22 of the plates 2 will extend somewhat around the teeth to provide a guide surface for this grinding, using the abrasive disc. It is, however, preferable to grind the interproximal size of the tooth in the manner described in my co-pending application Serial No. 52l,762, filed iuly 13, 1955, now Patent No. 2,793,438.

Once the shoulder is prepared in the manner shown in Fig. 6, the crown or porcelain jacket is fitted and mounted over the tooth in the conventional manner.

in certain cases the tooth may have an over-hanging portion 23, as shown in Fig. 7. In such instances, the tooth may be ground down first to an even cylindrical shape, using the cylindrical grinding wheel 18. The grinding wheel is merely placed with its lower guide surface 19 in contact with the plate 2 and the rotating grinding wheel pressed against the surface of the tube. Once the over-hanging portion 23 is ground down to the cylindrical shape as shown by the dotted lines 24, the abrasionfree portion 20 will contact the tooth and no further grinding may be effected. Thereafter, the groove 17 is cut with the grinding wheel 13, as shown in connection with Fig. 4 and after the cutting of the groove the remaining side wall is ground away to the depth of the groove 17, again using the grinding wheel in, as shown in connection with Fig. 5. I

While the invention has been described in detail with reference to the specific embodiments shown, variations and modifications will become apparent to the skilled artisan, which fall within the spirit of the invention and the scope of the appended claims.

I claim: Y

1. Device for aiding in the shoulder preparation of teeth, comprising a clamp having two opposing toothengaging guide plates dimensioned for engaging opposite sides of a tooth at or about the gum line, and being detachably connected to a pair of pivotally connected arms for exchange with different size guide plates, said guide plates defining substantially flat guide surfaces extending in a plane substantially normal to the tooth axis when said clamp is in tooth-engaging position and a tonguedepressing plate detachably connected to one of said pivotally connected arms.

2. Device for aiding in the shoulder preparation of teeth, comprising a clamp having two opposing t0othengaging guide plates dimensioned for engaging opposite sides of a tooth at or about the gum line, and being detachably connected to a pair of pivotally connected arms for exchange with different size guide plates, said guide plates defining substantially flat guide surfaces extending in a plane substantially normal to the tooth axis when said clamp is in tooth-engaging position and a checkretracting plate detachably connected to one of said pivotally connected arms.

References Cited in the file of this patent UNTTED STATES PATENTS 

